Dynamic quantity sensor

ABSTRACT

A dynamic quantity sensor includes a sensor board ( 10 ) having a movable portion ( 13 ) at one surface side thereof and a silicon layer ( 14 ) at another surface side thereof. The movable portion ( 13 ) is displaced under application of a dynamic quantity. The silicon layer ( 14 ) is separated from the movable portion ( 13 ) through an insulator ( 15 ). The dynamic quantity sensor also includes a circuit board ( 20 ) for transmitting/receiving electrical signals to/from the sensor board ( 20 ). The circuit board ( 20 ) is disposed to confront the one surface of the sensor board ( 10 ) through a gap portion ( 30 ) and cover the movable portion ( 13 ). The sensor board ( 20 ) and the circuit board ( 20 ) are bonded to each other around the gap portion ( 30 ) so that a bonding portion ( 40 ) is formed to substantially surround the gap portion ( 30 ) and thereby seal the gap portion ( 30 ).

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is based upon, claims the benefit of priorityof, and incorporates by reference, the contents of Japanese PatentApplication No. 2002-323896 filed on Nov. 7, 2002 and the contents ofJapanese Patent Application No. 2003-348253 filed on Oct. 7, 2003.

FIELD OF THE INVENTION

[0002] The present invention relates to a dynamic quantity sensor thatincludes a sensor board having a movable portion displaced underapplication of a dynamic quantity and that also includes a circuit boardfor transmitting/receiving electrical signals to/from the sensor board.

BACKGROUND OF THE INVENTION

[0003] Dynamic quantity sensors such as acceleration sensors or the likegenerally include a protection cap formed of resin, ceramic, silicon orthe like on a sensor board having a movable portion for covering themovable portion and thereby protecting the movable portion of the sensorboard (see Patent Document 1 (JP-A-10-253652), for example).

[0004] Furthermore, when a circuit board for transmitting/receivingelectrical signals to/from a sensor board is combined with the sensorboard and these boards are packaged by mold material such as resin orthe like, a structure is adopted that generally includes a sensor board10 having a protection cap CP fixed thereto and a circuit board 20mounted on a lead frame 50 as shown in FIG. 19.

[0005] However, in this case, a plurality of boards 10, 20 are mountedon the flat plane, which causes the package body to be designed in alarge size and need a protection cap CP. This accordingly leads toincreased costs.

[0006] A structure has been proposed in which a sensor board having amovable portion and a circuit board are laminated together so that themovable portion is covered by the circuit board to thereby omitting theprotection cap. Also, electrode bumps are formed on the circuit board sothat the circuit board and the sensor board are connected to each otherthrough the electrode bumps (see Patent Document 2 (JP-A-2001-227902),for example). In the laminate structure of the sensor board and thecircuit board through the electrode bumps as described above, the sensorbody can be miniaturized more than the case in which both the boards aremounted on the flat plane. However, there will still be a higher costbecause it is necessary to form electrode bumps on the circuit board.

SUMMARY OF THE INVENTION

[0007] Therefore, in view of the foregoing problem, an object of thepresent invention is to provide a dynamic quantity sensor equipped witha circuit board and a sensor board having a movable portion that can beimplemented at a low cost and compact size and without a protection cap.

[0008] In order to attain the above object, according to a first aspectof the present invention, a dynamic quantity sensor including a sensorboard having a movable portion equipped at one surface side thereof, themovable portion being displaced under application of a dynamic quantity,and a silicon layer equipped at another surface side thereof, thesilicon layer being separated from the movable portion through aninsulator, and a circuit board for transmitting/receiving electricalsignals to/from the sensor board, is characterized in that the circuitboard is disposed so as to confront one surface of the sensor boardthrough a gap portion and to cover the movable portion. The sensor boardand the circuit board are bonded to each other around the gap portion sothat the bonding portion is formed to surround the gap portion.

[0009] According to the dynamic quantity sensor described above, boththe circuit board and the sensor board are bonded to each other andlaminated at a low cost by merely disposing a bonding member betweenboth the boards. As another method, the bonding between both the boardscan be performed without any bonding member by using direct bondingbetween both the boards. The movable portion of the sensor board iscovered by the circuit board through the gap portion and the peripheryof the gap portion is surrounded by the bonding portion, so that themovable portion is properly protected from external forces and thus noprotection cap is needed.

[0010] Furthermore, the sensor board has the movable portion which isequipped at one surface side thereof so as to be displaced underapplication of a dynamic quantity, and the silicon layer which isequipped at the other surface side thereof so as to be separated fromthe movable portion by an insulator 15. Therefore, the electrical andmagnetic shielding at the sensing portion containing the movable portioncan be properly performed.

[0011] Accordingly, according to the present invention, the dynamicquantity sensor equipped with the sensor board having the movableportion and the circuit board can be implemented at a low cost and acompact size while omitting a protection cap.

[0012] According to a second aspect of the present invention, the sensorboard and the circuit board may be electrically connected to each otherby bonding wires to perform the electrical connection between bothboards at a low cost.

[0013] According to a third aspect of the present invention, in thedynamic quantity sensors of the first and second aspects of the presentinvention, the sensor board and the circuit board 20 may be sealinglywrapped by mold material. Even in this case, the movable portion isprotected by the circuit board and the bonding portion and thus the moldmaterial can be properly prevented from entering into the movableportion.

[0014] According to a fourth aspect of the present invention, the sensorboard and the circuit board may be sealed by soft material softer thanthe mold material and the outside of the soft material may be wrapped bythe mold material. When the sensor board and the circuit board aresealed by the mold material, stress caused by temperature variation orthe like in use is applied to the elements thus sealed. However, softmaterial as described above effectively moderates the stress by beinginterposing between the circuit and the mold material.

[0015] According to a fifth aspect of the present invention, a recessportion is formed on a surface of the circuit board facing the sensorboard and the gap portion is constructed by the recess portion. Also,the bonding portion is formed at sites other than the recess portion onthe circuit board. With this construction, the gap portion can beproperly formed by the recess portion formed on the circuit board.

[0016] According to a sixth aspect of the present invention, the sensorboard may be designed to have a plurality of movable portions formed onone surface thereof. In this case, the circuit board covers each movableportion through the gap portion whose periphery is surrounded by thebonding portion. When a plurality of movable portions are equipped onthe sensor board, the area of the gap portion between the circuit boardand the sensor board is increased to cover the plurality of movableportions.

[0017] According to a seventh aspect of the present invention, a rimportion abutting against the sensor board is formed at a site on thecircuit board which faces areas other than the area having the pluralityof movable portions formed therein on the sensor board. In this case,the rim portion effectively mechanically supports both of the boards.

[0018] According to an eighth aspect of the present invention, when thesensor includes a lead frame for transmitting electrical signals to anexterior device, the sensor board can be bonded to the lead frame onanother surface opposite to one surface of the sensor board facing thecircuit board.

[0019] According to a ninth aspect of the present invention, in the casein which the sensor includes the lead frame for transmitting theelectrical signals to an exterior device, an overhang area which doesnot face the sensor board and overhangs from the sensor board isequipped on the surface of the circuit board facing the sensor board.The lead frame may be bonded to the overhang area on the circuit board.The construction of this aspect is effective to such a case that thecircuit board is larger than the sensor board and thus the circuit boardpartly overhangs from the sensor board. According to this construction,it is unnecessary to directly fix the sensor board to the lead framewhich is normally formed of metal. This construction leads to theimproved results of a sensor board that hardly suffers from the effectsof thermal stress caused by temperature variation or the like and thatachieves more stable sensor characteristics.

[0020] According to a tenth aspect of the present invention, an overhangarea which does not face the sensor board and that overhangs from thesensor board is equipped on the surface of the circuit board which facesthe sensor board, and a separate board separated from the sensor boardis equipped to the overhang area on the circuit board so that thecircuit board is supported by the separate board. The construction ofthis aspect is effective to such a case that the circuit board is largerthan the sensor board and thus the circuit board partially overhangsfrom the sensor board. According to this construction, the overhang areaof the circuit board is supported by the separate board so that thecircuit board can be stably supported and that the wire-bonding to thecircuit board can be effectively performed.

[0021] According to an eleventh aspect of the present invention, aplurality of sensor boards may be bonded to the circuit board. When thecircuit board is larger than one sensor board and includes the pluralityof sensor boards, an area overhanging from one sensor board exists onthe circuit board. However, according to the eleventh aspect of thepresent invention, another sensor board brings the same effect as theseparate board as the tenth aspect of the present invention. That is,according to this aspect, in addition to the effect as the tenth aspect,the plurality of sensor boards can be arranged.

[0022] According to a twelfth aspect of the present, a dynamic quantitysensor including a sensor board having a movable portion equipped at onesurface side thereof, the movable portion being displaced underapplication of a dynamic quantity, and a circuit board fortransmitting/receiving electrical signals to/from the sensor board ischaracterized in that the circuit board is disposed so as to confrontone surface of the sensor board through a gap portion and to cover themovable portion. The sensor board and the circuit board are partiallybonded to each other around the gap portion.

[0023] According to this aspect, both the boards can be bonded to eachother at a low cost and laminated by merely disposing a bonding memberbetween the circuit board and the sensor board. In addition, the movableportion of the sensor board is covered by the circuit board through thegap portion so that the movable portion can be properly protected fromthe exterior and thus no protection cap is needed.

[0024] Therefore, the dynamic quantity sensor equipped with the sensorboard having the movable portion and the circuit board can beimplemented at a low cost and a compact size while omitting theprotection cap.

[0025] The reference numerals in parentheses representing the respectivemeans described above are provided as examples to show the correspondingrelationship with specific means described in the following embodiments.

[0026] Further areas of applicability of the present invention willbecome apparent from the detailed description provided hereinafter. Itshould be understood that the detailed description and specificexamples, while indicating the preferred embodiment of the invention,are intended for purposes of illustration only and are not intended tolimit the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The above and other objects, features and advantages of thepresent invention will become more apparent from the following detaileddescription made with reference to the accompanying drawings. In thedrawings:

[0028]FIG. 1 is a schematic cross-sectional view showing an accelerationsensor according to a first embodiment of the present invention;

[0029]FIGS. 2A and 2B are enlarged views of the sensor board and circuitboard shown in FIG. 1;

[0030]FIG. 3 is a schematic cross-sectional view showing a modificationto the first embodiment;

[0031]FIG. 4 is a schematic cross-sectional view showing anothermodification to the first embodiment;

[0032]FIG. 5 is a schematic cross-sectional view showing an accelerationsensor according to a second embodiment of the present invention;

[0033]FIG. 6 is a schematic cross-sectional view showing an accelerationsensor according to a third embodiment of the present invention;

[0034]FIG. 7 is a schematic cross-sectional view showing a modificationto the third embodiment;

[0035]FIG. 8 is a schematic cross-sectional view showing an accelerationsensor according to a fourth embodiment of the present invention;

[0036]FIG. 9 is a plan view of the circuit board in FIG. 8 when viewedfrom the top side;

[0037]FIG. 10 is a schematic cross-sectional view showing a modificationto the fourth embodiment;

[0038]FIG. 11 is a schematic cross-sectional view showing anacceleration sensor according to a fifth embodiment of the presentinvention;

[0039]FIG. 12 is a plan view of the accelerator in FIG. 11 when viewedfrom the top side;

[0040]FIG. 13 is a schematic cross-sectional view showing anacceleration sensor according to a sixth embodiment of the presentinvention;

[0041]FIG. 14 is a schematic cross-sectional view showing anacceleration sensor according to a seventh embodiment of the presentinvention;

[0042]FIG. 15 is a schematic cross-sectional view showing a modificationof the seventh embodiment;

[0043]FIG. 16 is a schematic cross-sectional view showing anacceleration sensor according to an eighth embodiment of the presentinvention;

[0044]FIGS. 17A and 17B are diagrams showing the construction of themain part of an acceleration sensor according to another alternativeembodiment of the present invention;

[0045]FIG. 18 is a diagram showing the construction of the main part ofan acceleration sensor according to a ninth embodiment of the presentinvention; and

[0046]FIG. 19 is a perspective view showing a conventional generalconstruction of a dynamic quantity sensor having a sensor board and acircuit board.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0047] Preferred embodiments according to the present invention will bedescribed hereunder. In the following embodiments, the same parts arerepresented by same reference numerals to simplify the descriptionthereof.

[0048] (First Embodiment)

[0049]FIG. 1 is a schematic cross-sectional view showing an accelerationsensor (sensor) S1 as a dynamic quantity sensor according to a firstembodiment of the present invention. FIG. 2A is an enlarged view showinga sensor board 10 and a circuit board 20 which are laminated to beunified into one body in FIG. 1.

[0050] The sensor S1 includes a sensor board 10 having a movable portion13 disposed at one surface side (or top surface side) 11. The movableportion 13 is displaced under application of acceleration (dynamicquantity). The sensor S1 further includes a circuit board 20 fortransmitting and receiving electrical signals to and from the sensorboard 10.

[0051] In the first embodiment the sensor board 10 and circuit board 20are preferably implemented as chips by subjecting a wafer-type materialto dicing-cutting or the like. The circuit board 20 is preferably an ICchip formed of silicon semiconductor or the like. A surface (or topsurface) 21 of the circuit board 20 serves as a circuit-forming surfaceon which circuit elements are formed. The circuit board 20 is disposedso that its back surface 22 at the opposite side to the circuit-formingsurface 21 faces the one surface 11 of the sensor board 10 through a gapportion 30 while covering the movable portion 13.

[0052] The back surface 22 of the circuit board 20 is bonded to the onesurface 11 of the sensor board 10 through a bonding member around thegap portion 30 to thereby form a bonding portion 40. The bonding portion40 is designed to have an annular shape that substantially surrounds theperiphery of the gap portion 30 to thereby sealing the gap portion 30.

[0053] Referring to FIG. 1, the bonding member constituting the bondingportion 40 functions as a spacer. More particularly, the bonding portion40 results in the formation of a gap portion 30 that prevents themovable portion 13 of the sensor board 10 from coming into contact withthe back surface 22 of the circuit board 20. An adhesive agentcontaining low-melting glass, beads or the like, or material having athickness as a spacer such as an adhesive sheet or the like may be usedas the bonding member.

[0054] Returning to FIG. 2A, an exemplary implementation of the sensorboard 10 of the first embodiment will be discussed. The sensor board 10is designed by laminating plural silicon layers, silicon oxide films,etc. The detailed construction of the sensor board 10 as described aboveis disclosed in FIG. 7 of JP-A-9-129898, the contents of which areincorporated by reference.

[0055] In the sensor board 10, a first silicon oxide film 15 is formedon a first silicon layer 14 by thermal oxidation or the like. Anelectrically conductive layer 16 formed from polysilicon is formed onthe first silicon oxide film 15 by a CVD (Chemical Vapor Deposition)method or the like. A second silicon oxide film 17 is formed on thefirst silicon oxide film 15 by CVD, a sputtering method, a vapordeposition method or the like. Then, a second silicon layer 18 is formedon the second silicon oxide film 17 by CVD or the like to therebyachieve a laminate structure. The electrically conductive layer 16 maybe formed not only from polysilicon, but also from a high melting pointmetal such as tungsten, molybdenum or the like, or silicide (a compoundof silicon and the above metal) or the like.

[0056] Next, grooves 18 a are formed in the second silicon layer 18 inconformity with a pattern of the movable portion 13, a fixed portion,etc. The second silicon oxide film 17 is then etched and removed inproper areas through the grooves 18 a. The second silicon layer 18 isresultantly formed into the movable portion 13 and the fixed electrodecorresponding to the fixed portion, etc. in the areas from which thesecond silicon oxide film 17 is removed.

[0057] The movable portion 13 of this embodiment is preferably formed asa cantilevered portion supported at only one site and is disposed toface a fixed electrode (not shown for ease of illustration) through agap in the vertical direction to the sheet plane of FIG. 2A. Whenacceleration is applied to the movable portion 13, it is displaced inthe vertical direction to the sheet plane of FIG. 2A, so that theinterval between the movable portion 13 and the fixed electrode isvaried. The variation of the interval between the movable portion 13 andthe fixed electrode causes variation of the capacitance between both theelectrodes, and thus the applied acceleration is detected on the basisof an electrical signal caused by the capacity variation between boththe electrodes.

[0058] As mentioned above, the movable portion 13 is preferablysupported at only one site thereof (i.e., cantilevered) in thisembodiment. However, the movable portion 13 may also be supported at twosites thereof (i.e., straddled) or at three or more sites thereof. Inthis case, the movable portion 13 and the fixed electrode, that is, thesensing portion is covered by the circuit board 20 in the sensor board10 as shown in FIG. 2A, and electrical signals from the sensing portionare picked up through the electrically conductive layer 16 extendingfrom the position just below the circuit board 20 to the outside of thecircuit board 20.

[0059] The electrically conductive layer 16 is conducted to the secondsilicon layer 18 at a site overhanging from the position just blow thecircuit board 20. Pads 19 formed of aluminum or the like are formed onthe surface of the second silicon layer 18 at this site (the surface 11of the sensor board 10). The pads 19 are subjected to wire bonding orthe like to electrically connect the sensor board 10 and the circuitboard 20 or the lead frame 50.

[0060] Referring to FIG. 2B, an exemplary implementation of the sensorboard 10 and its sensing portion will be discussed. In this example, anSOI structure having a laminate structure including a first siliconlayer 26, a silicon oxide layer 27 and a second silicon layer 28 is usedto implement the circuit board 20. Circuit elements are formed on thefirst silicon layer 26 and the second silicon layer 28 is used as ashield layer for the sensing portion. The second silicon layer 28 andthe sensor board 10 are electrically connected to each other by using anelectrically conductive adhesive agent as the bonding portion 40. Atthis time, the area of the sensing portion which is bonded by thebonding portion 40 is wire-bonded to a bonding pad equipped in an area(not shown) to set the area concerned to a constant voltage such as 0 V(ground) or the like.

[0061] The sensing portion (electrode portion) of the capacitance typeaccelerator of this embodiment can be shielded when the first siliconlayer 14 as a support portion in the sensor board 10 is bonded to a leadframe 50 (described later) by an electrically conductive adhesive agentor the like to set the first silicon layer 14 to 0 V. This is preferablebecause the capacitance type sensor handles a minute variation ofcapacitance. This implementation can provide a more stable output evenwhen resin mold is applied.

[0062] More particularly, in this embodiment, as shown in FIG. 2, thesensor board 10 is equipped with the movable portion 13 at the onesurface side thereof so that the movable portion 13 is displaced byapplication of a dynamic quantity, and also the first silicon layer(silicon layer) 14 at the other surface side thereof so that the firstsilicon layer 14 is separated from the movable portion 13 by the firstsilicon oxide film (insulator) 15. Therefore, the shielding of thesensing portion containing the movable portion 13 can be properlyperformed.

[0063] In this embodiment, the electrical connection between the sensorboard 10 and the external device as described above is performed byproviding the lead frame 50 through which electrical signals from thesensor board 10 are transmitted as shown in FIG. 1. The lead frame 50 isformed of metal such as copper or the like, or metal which is matched inthermal expansion coefficient with the silicon board such as, forexample, 4-2 Alloy, covar or the like.

[0064] Another surface 12 at the opposite side to the one surface 11 ofthe sensor board 10 facing the back surface 22 of the circuit board 20is bonded to the lead frame 50 through an adhesive member 60 such asadhesive agent, adhesive sheet or the like.

[0065] As shown in FIGS. 1, 2A and 2B, the electrical connection amongthe sensor board 10, the circuit board 20 and the lead frames 50 isperformed through the pads 19 of the sensor board 10 and the pads 23formed on the surface 21 of the circuit board 20 and through the bondingwires of gold, aluminum or the like formed by wire-bonding.

[0066] A mold material 80 wraps and seals the sensor board 10, thecircuit board 20, the bonding wires 70 and parts of the lead frame 50.The mold material 80 is preferably mold resin such as generally-usedepoxy resin or the like.

[0067] An exemplary methodology for manufacturing the accelerationsensor S1 as described above will now be discussed. The circuit board 20and the sensor board 10, which are unified into one body through theboding member, are mounted and fixed through the adhesive member 60 ontothe lead frame 50. Alternatively, the sensor board 10 is mounted andfixed through the adhesive member 60 on to the lead frame 50, and thenthe circuit board 20 is mounted and fixed through the bonding member onthe sensor board 10.

[0068] Thereafter, the electrical connection is performed among thesensor board 10, the circuit board 20 and the lead frame 50 by the wirebonding, and then the molding process using the mold material 80 iscarried out by using a metal mold. Thereafter, segmentalization or thelike of the lead frame 50 is carried out to complete the accelerationsensor S1 shown in FIG. 1.

[0069] In the acceleration sensor S1 described above, when accelerationis applied, the electrical signal corresponding to the appliedacceleration is output from the sensor board 10 by the action of themovable portion 13 described above. This electrical signal is subjectedto signal processing such as amplification, adjustment, etc. in thecircuit board 20, and then transmitted from the lead frames 50 throughthe bonding wires 70 to the outside.

[0070] According to the acceleration sensor S1 shown in FIG. 1, both thecircuit board 20 and the sensor board 10 can be bonded to each other andlaminated at a low cost by merely disposing the bonding member betweenboth the boards 20 and 10. The movable portion 13 of the sensor board 10is covered by the circuit board 20 through the gap portion 30. Theperiphery of the gap portion 30 is sealingly surrounded by the bondingportion 40, so that the movable portion 13 is properly protected from anexternal device (or generally from external disturbances) and noprotection cap is needed.

[0071] As another method, the bonding between both the boards 10, 20 canbe performed without any bonding member by using direct bonding betweenboth of the boards 10, 20.

[0072] Furthermore, as described above, the sensor board 10 has themovable portion 13 at one surface side thereof so that the movableportion 13 is displaced under application of a dynamic quantity, and thesilicon layer 14 equipped at the other surface side thereof so that itis separated from the movable portion 13 by an insulator 15. Therefore,the shielding of the sensing portion containing the movable portion 13can be properly performed.

[0073] Therefore, according to the acceleration sensor S1 shown in FIG.1, a dynamic quantity sensor can be implemented at a low cost andcompact size with no protection cap.

[0074] Furthermore, according to the sensor S1, the sensor board 10 andthe circuit board 20 are electrically connected to each other throughthe bonding wires 70, and the electrical connection between both theboards 10, 20 can also be implemented at a low cost.

[0075] The electrical connection between the sensor board 10 and thecircuit board 20 may be performed in a manner other than the directconnection using bonding wires between both the boards. For example, thelead frame 50 which is electrically connected to the circuit board 20through the bonding wires or the like may be connected to the sensorboard 10 by wire bonding to thereby electrically connect both the boards10, 20 through the lead frame.

[0076] Furthermore, in the acceleration sensor S1 shown in FIG. 1, thesensor board 10, the circuit board 20 and the bonding wires 70 arewrapped and sealed by the mold material 80. In this case, the movableportion 13 is protected by the circuit board 20 and the bonding portion40 so that the mold material 80 is properly prevented from entering thearea of the movable portion 13.

[0077]FIG. 3 is a schematic cross-sectional view showing another exampleof the sensor board 10 according to a first modification to the firstembodiment. In the sensor board 10, insulating material 18 b formed ofsilicon oxide or the like may be formed by CVD or the like is embeddedaround the conductive layer 16 and the second silicon layer 18 havingthe pads 19 formed thereon to keep electrical insulation around theconductive layer 16.

[0078] In the example of FIG. 1, the circuit board 20 is disposed sothat the back surface 22 at the opposite side to the surface(circuit-formed surface) 21 of the circuit board 20 faces the onesurface 11 of the sensor board 10. However, the surface 21 of thecircuit board 20 and the one surface 11 of the sensor board 10 may beconfronted to each other as shown in FIG. 4. In this case, the backsurface 22 of the circuit board 20 fixedly adheres to the lead frame 50.

[0079] In FIG. 4, the area in which the movable portion 13 and the fixedelectrode are formed at the one surface 11 side of the sensor board 10is represented by a sensing portion 13 a, and the gap portion 30 throughwhich the sensing portion 13 a is partitioned from the outside is formedby the surface 21 of the circuit board 20 and the bonding portion 40.

[0080] (Second Embodiment)

[0081] Referring to FIG. 5, a second embodiment of the accelerationsensor S2 will now be discussed. In this embodiment, the sensor board10, the circuit board 20 and the bonding wires 70 are sealed by a softmaterial 85 softer than the mold material 80, and the outside of thesoft material 85 is wrapped by the mold material 80.

[0082] More particularly, the acceleration sensor S2 is designed so thatthe soft material 85 is interposed between the mold material 80 and eachof the sensor board 10, the circuit board 20 and the bonding wires 70 inthe acceleration sensor S1 shown in FIG. 1. The soft material 85 may besilicone gel, soft resin, rubber or the like; however, the soft materialshould be softer than the mold material 80. The sealing targets 10, 20,70 are coated with the soft material 85 in advance, and then the moldingprocess using the mold material 80 is applied to thereby form theacceleration sensor S2 shown in FIG. 5.

[0083] When the sensor board 10, the circuit board 20 and the bondingwires 70 are sealed by the mold material 80, stress caused by thetemperature variation is applied to these sealing targets 10, 20, 70.However, according to this embodiment, this stress is effectivelymoderated by interposing the soft material 85.

[0084] (Third Embodiment)

[0085] Referring to FIG. 6, a third embodiment of the accelerationsensor S3 will be discussed. The acceleration sensor S3 is achieved byequipping a recess portion 24 to the circuit board 20 of theacceleration sensor S1 as shown in FIG. 1. The other surface 12 at theopposite side to the one surface 11 of the sensor board 10 facing theback surface 22 of the circuit board 20 is bonded to the lead frame 50through an adhesive member such as adhesive agent, adhesive sheet or thelike (not shown for ease of illustration).

[0086] In this embodiment, as shown in FIG. 6, a recess portion 24 isformed on the confronting face (back surface) 22 of the circuit board 20which confronts the sensor board 10, and the gap portion is formed bythe recess portion 24. The bonding portion 40 is formed at a sitedifferent than the recess portion 24 of the circuit board 20.

[0087] A thin portion is partially formed on the back surface 22 of thecircuit board 20 by wet or dry etching of silicon or the like to formthe recess portion 24. The etching for forming the recess portion 24 maybe performed as a lump in every wafer.

[0088] The thick portion other than the recess portion 24 of the circuitboard 20 is bonded to the one surface of the sensor board 10 by usingadhesive agent or the like, so that the bonded portion serves as theannular bonding portion 40. As described above, the gap portion 30 inthe recess portion 24 is sealed, and the sensing portion 13 a on thesensor board 10 is protected from the external. That is, the movableportion 13 is protected from the external.

[0089] In this case, the gap portion 30 can be properly formed by therecess portion 24 formed on the circuit board 20. Therefore, it isunnecessary to dispose the bonding member constituting the bondingportion 40 which is thick enough to function as a spacer as in the caseof the first embodiment.

[0090] Referring to FIG. 7, a first modification to the third embodimentwill be discussed. The sensor board 10 may be designed so that thesensing portion 13 a containing the movable portion 13 is formed at aposition deeper than the one surface 11 of the sensor board 10. Thesensor board 10 as described above is formed in the following manner orthe like. That is, an area in which the sensing portion 13 a will beformed is recessed in advance by etching, and then the sensing portion13 a is formed in the area.

[0091] In the sensor board 10 as described above, the gap portion 30 isformed by the sensing portion 13 a which is recessed from the onesurface 11, so that the gap portion 30 can be properly formed without aneed to form the recess portion 24 in the circuit board 20 as in FIG. 6.

[0092] As described above, according to this embodiment, when the gapportion 30 is formed, the confronting face of the circuit board 20 orthe sensor board 10 is designed to have a recess portion, whereby thegap portion can be properly formed.

[0093] (Fourth Embodiment)

[0094] Referring to FIG. 8, a fourth embodiment of an accelerationsensor S4 will be discussed. In this embodiment, a plurality of movableportions 13 are disposed on the one surface 11 of the sensor board 10.

[0095] As shown in FIGS. 8, 9, two sensing portions 13 a, each of whichcontaining the movable portion 13, are formed on the one surface 11 ofthe sensor board 10. In this case, the other surface 12 at an oppositeside to the one surface 11 of the sensor board 10 facing the backsurface 22 of the circuit board 20 is bonded to the lead frame 50through an adhesive member such as adhesive agent, adhesive sheet or thelike (not shown).

[0096] When the two sensing portions 13 a are formed as described above,they may be designed so that one of the sensing portions 13 a detectsacceleration in the X-axis direction while the other sensing portion 13a detect the acceleration in a Y-axis direction perpendicular to theX-axis direction as indicated by the axes in FIG. 9. More generally, thetwo sensing portions 13 a can implement a multi-axial sensor. If threeor more sensing portions are equipped, further multi-axial detectionscan be performed.

[0097] In this case, the recess portion 24 is formed on the back surface22 of the circuit board 20 facing the one surface 11 of the sensor board10, and each of the sensing portions 13 a is covered through the gapportion 30 by the recess portion 24.

[0098] A thick portion of the circuit board 20 (the portion other thanthe recess portion 24) is bonded to the one surface of the sensor board10 by using adhesive agent or the like, and the portion thus bondedserves as the bonding portion 40. The bonding portion 40 is formed so asto substantially if not completely surround the gap portion 30 tothereby seal the gap portion 30.

[0099] Furthermore, when a plurality of movable portions 13 are disposedon the sensor board 10 as in this embodiment, the area of the gapportion 30 between the circuit board 20 and the sensor board 10 isincreased to cover the plurality of movable portions 13.

[0100] Referring to FIG. 10, a first modification to the fourthembodiment will be discussed. In this case, a rim portion 25 whichprojects from the bottom portion of the recess portion 24 and abutsagainst the sensor board 10 may be formed at a site of the circuit board20 which faces an area other than the area of the sensor board 10 wherethe plurality of movable portions 13 are formed.

[0101] The rim portion 25 may be formed as a part of the circuit board20 or it may be formed as a spacer such as low-melting glass, adhesiveagent or the like. With this construction, the rim portion 25 caneffectively support both the boards 10, 20 mechanically even when therecess portion 24 has a large area.

[0102] (Fifth Embodiment)

[0103] Referring to FIGS. 11-12, a fifth embodiment of the accelerationsensor S5 will be discussed. FIG. 12 is a plan view of the sensor board10, the circuit board 20 and the lead frame 50 of FIG. 11 which areviewed from the upper side. Hatching is applied to FIG. 12 foridentification for the sake of convenience.

[0104] In this embodiment, the circuit board 20 is designed to be largerthan or substantially equal to the sensor board 10. This construction iseffective for the case in which the circuit board 20 overhangs thesensor board 10.

[0105] As shown in FIGS. 11 and 12, the overhang area 20 a which doesnot face the one surface 11 of the sensor board 10 and overhangs fromthe sensor board 10 exists on the back surface 22 of the circuit board20 facing the sensor board 10. The lead frame 50 is bonded to theoverhang area 20 a of the circuit board 20.

[0106] In this case, as shown in FIGS. 11 and 12, an opening portion 51is formed as a board mount portion (chip mount portion) in the leadframe 50, and the sensor board 10 is mounted in the opening portion 51.

[0107] This construction can be manufactured by mounting and fixing theunified circuit board 20 and sensor board 10 onto the lead frame 50through an adhesive member. Alternatively, it may be manufactured bymounting and fixing the circuit board 20 onto the lead frame 50 throughan adhesive member and then fixing the sensor board 10 to the circuitboard 20 through a bonding member.

[0108] According to this embodiment, the sensor board 10 formed ofsilicon or the like is not directly fixed to the lead frame of metal.Resultantly, the sensor board 10 hardly suffers from the effects ofthermal stress occurring due to temperature variation caused by thedifference in thermal expansion coefficient between the sensor board 10and the lead frame 50. This contributes to stabilization of the sensorcharacteristics such as the characteristic of the movable portion 13,etc.

[0109] Furthermore, in the acceleration sensor S5 shown in FIG. 11, itis preferable that the sensor board 10 and the circuit board 20 arecoated by the soft material 85. Therefore, the thermal stress effect ofthe mold material 80 on the sensor board 10 can be moderated.

[0110] (Sixth Embodiment)

[0111]FIG. 13 is a schematic cross-sectional view showing theconstruction of an acceleration sensor S6 as a dynamic quantityaccording to a sixth embodiment of the present invention. Thisembodiment is a modification of the fifth embodiment.

[0112] When the circuit board 20 is larger than or substantially equalto the sensor board 10 and thus overhangs from the sensor board 10, theother surface 12 at the opposite side to the one surface 11 of thesensor board 10 which faces the circuit board 20 may be bonded to thelead frame 50.

[0113] (Seventh Embodiment)

[0114]FIG. 14 is a schematic cross-sectional view showing anacceleration sensor S7 as a dynamic quantity sensor according to aseventh embodiment of the present invention.

[0115] This embodiment is a modification of the sixth embodiment. Inthis embodiment, the overhang area 20 a of the circuit board 20 isequipped with a separate board 90 separated from the sensor board 10,and the circuit board 20 is supported by the separate board 90.

[0116] The separate board 90 may be a second circuit board which is anIC chip separated from the circuit board 20, or a dummy chip formed of aplate-shaped silicon member or the like. The separate board 90 isadhesively fixed to the lead frame 50; however, it is not necessarilybonded to the circuit board 20.

[0117] According to this embodiment, since the overhang area 20 a of thecircuit board 20 is supported by the separate board 90, the circuitboard 20 can be stably supported, and bonding performance can be easilysecured in such a case that wire bonding is carried out at the sitecorresponding to the overhang area 20 a of the circuit board 20, forexample.

[0118] In FIG. 14, the sensor board 10 and the separate body 90 arebrought into contact with each other. However, as shown in FIG. 15, thesensor board 10 and the separate board 90 may be disposed so as to bespaced from each other through a separating portion 91.

[0119] (Eighth Embodiment)

[0120]FIG. 16 is a schematic cross-sectional view showing anacceleration sensor S8 as a dynamic quantity sensor according to aneighth embodiment of the present invention.

[0121] This embodiment is a modification of the seventh embodiment. Inplace of the separate board, second, third, or more sensor boards 10 areequipped to the overhang area 20 a of the circuit board 20, and bondedto the circuit board 20 to support the circuit board 20.

[0122] More particularly, according to this embodiment, each of theplurality of sensor boards 10 is equipped with a movable portion 13 atone surface side thereof so that the movable portion 13 is sealed by acommon circuit board 20 and a bonding portion 40 so as to face thecommon circuit board 20 through the gap portion 30 and be assembled andunified with the common circuit board 20.

[0123] When the circuit board 20 is larger than one sensor board 10 andthe sensor includes a plurality of sensor boards 10, an overhang areaexists for one sensor board 10 on the circuit board 20. In this case,the other sensor boards 10 have the same effect as the separate board.

[0124] Furthermore, according to this embodiment, a plurality of sensorboards 10 can be arranged by one circuit board 20, and also amulti-axial sensor which can detect in the multi-axial directions can beformed by the sensor boards 10 separated from one another.

[0125] (Other Embodiments)

[0126] The second and subsequent embodiments described aboveappropriately use the construction that the surface 21 of the circuitboard 20 and the one surface 11 of the sensor board 10 confront eachother.

[0127] Furthermore, the sensor board 10 and the circuit board 20 whichare laminated and fixed as described with respect to each of theembodiments may be mounted on a print board or ceramic board or in aceramic package in the form of a bare chip in which both the boards areunified.

[0128] When the bare chip is put on a ceramic board or print board withno resin molding and they are placed in and air-tightly sealed inanother package, or when the bare chip is put in a ceramic package, itis unnecessary that the bonding portion 40 between the circuit board 20and the sensor board 10 be designed in such an air-tight structure as tosurround the gap portion 30, and it is sufficient to secure the gapportion 30 and the bonding strength.

[0129] The above embodiment is shown in FIGS. 17A and 17B, wherein FIG.17A is a cross-sectional view and FIG. 17B is a plan view which isviewed from the top side. The bonding portion 40 is partially equippedto the corner portions of the circuit board 20, and the sensor board 10and the circuit board 20 are partially bonded to each other on theperiphery of the gap portion 30. In this case, the movable portion 13 ofthe sensor board 10 is also covered by the circuit board 20 through thegap portion 30, so that the movable portion 13 is appropriatelyprotected from the external.

[0130]FIG. 18 is a cross-sectional view schematically showing theconstruction of an acceleration sensor according to another embodimentof the present invention.

[0131] In the embodiment shown in FIG. 18, the circuit board 20 isdisposed so that the back surface 22 thereof confronts one surface 11 ofthe sensor substrate 10 through the gap portion 30 so as to cover thesensing portion 13 a. The bonding portion 40 surrounding the gap portion30 is formed by anodic bonding through a glass layer 100 formed on theone surface 11 of the sensor substrate 10.

[0132] The device of this embodiment is formed as follows. After an Alwiring portion (not shown) is formed, by using the sputtering method,the CVD method or the like, for example, a glass layer 100 is formedover the whole surface of wafer on which many acceleration sensors(dynamic quantity sensors) are formed. In this embodiment, for example,borosilicate glass is formed, and then the surface thereof is polishedby CMP or the like so that it is finished to have a mirror-surfacestate.

[0133] Subsequently, the glass layer 100 is partially removed byphotolithographic etching at a site which will serve as a sensingportion containing a movable portion and also at a Al-pad forming site101 to be subjected to wire bonding. Subsequently, the movable portion13, etc. are formed at the site of the sensing portion 13 a by dryetching or the like.

[0134] The mirror-polished back surface 22 of the circuit board 20having circuits formed thereon and the upper surface of the glass layer100 which is formed on the sensor board 10 and subjected tomirror-surface polishing are subjected to anodic bonding. As describedabove, both the boards 10, 20 may be directly bonded to each otherwithout being connected to each other through adhesive agent or a metalbarrier layer.

[0135] Furthermore, if the mirror surfaces are smoothened with highprecision, they can be directly and firmly bonded to each other withoutanodic bonding by merely bringing them into contact with each other. Inthis case, the direct bonding progresses more surely by setting thetemperature from 400° C. to 500° C.

[0136] This embodiment may be also applied to the cases shown in FIGS. 7and 8. More particularly, FIG. 7 shows the structure that the movableportion 13 is located at a lower position than the one surface 11 of thesensor substrate 10, and FIG. 8 shows the structure that the recessportion 24 is formed on the back surface 22 of the circuit board 20.

[0137] In these cases, the silicon face can be directly exposed as thecontact face of the sensor board 10, and thus it can be directed bondedto the silicon face of the back surface 22 of the circuit board 20 in asilicon-silicon direct bonding style. Furthermore, thermal oxide filmmay be formed on at least one of the silicon faces of both the boards 10and 20 to perform the direct bonding.

[0138] The present invention is applicable to not only the accelerationsensor, but also dynamic quantity sensors such as an angular velocitysensor, a pressure sensor, etc.

[0139] The description of the invention is merely exemplary in natureand, thus, variations that do not depart from the gist of the inventionare intended to be within the scope of the invention. Such variationsare not to be regarded as a departure from the spirit and scope of theinvention.

What is claimed is:
 1. A dynamic quantity sensor comprising: a sensorboard including a movable portion at one surface side thereof and asilicon layer at another surface side thereof, wherein the movableportion is displaced under application of a dynamic quantity and thesilicon layer is separated from the movable portion by an insulator; anda circuit board for transmitting to and receiving electrical signalsfrom the sensor board, wherein the circuit board is disposed to confrontthe one surface of the sensor board through a gap portion and to coverthe movable portion, and the sensor board and the circuit board arebonded to each other around the gap portion so that a bonding portion isformed that substantially surrounds the gap portion.
 2. The dynamicquantity sensor according to claim 1, wherein the sensor board and thecircuit board are sealingly wrapped by mold material.
 3. The dynamicquantity sensor according to claim 1, wherein: a recess portion isformed on a surface of the circuit board facing the sensor board tothereby form the gap portion; and the bonding portion is formed at sitesother than the recess portion on the circuit board.
 4. The dynamicquantity sensor according to claim 1, wherein the sensor board isdesigned to have a plurality of movable portions formed on one surfacethereof, and the circuit board covers each of the plurality of movableportions through the gap portion.
 5. The dynamic quantity sensoraccording to claim 1, further comprising a lead frame for transmittingelectrical signals to an exterior, wherein the sensor board is bonded tothe lead frame on another surface opposite to the one surface of thesensor board facing the circuit board.
 6. The dynamic quantity sensoraccording to claim 1, further comprising a lead frame for transmittingthe electrical signals to an exterior, wherein an overhang area thatdoes not face the sensor board and that overhangs from the sensor boardis equipped on the surface of the circuit board that faces the sensorboard, and the lead frame is bonded to the overhang area on the circuitboard.
 7. The dynamic quantity sensor according to claim 1, wherein anoverhang area that does not face the sensor board and that overhangsfrom the sensor board is equipped on the surface of the circuit boardthat faces the sensor board, and a separate board separated from thesensor board is equipped to the overhang area on the circuit board sothat the circuit board is supported by the separate board.
 8. Thedynamic quantity sensor according to claim 1, wherein the sensor boardand the circuit board are electrically connected to each other bybonding wires.
 9. The dynamic quantity sensor according to claim 1,wherein the sensor board and the circuit board are sealingly wrapped bymold material.
 10. The dynamic quantity sensor according to claim 9,wherein the sensor board and the circuit board are sealed by softmaterial softer than the mold material, and the outside of the softmaterial is wrapped by the mold material.
 11. The dynamic quantitysensor according to claim 10, wherein: a recess portion is formed on asurface of the circuit board facing the sensor board to thereby form thegap portion; and the bonding portion is formed at sites other than therecess portion on the circuit board.
 12. The dynamic quantity sensoraccording to claim 10, wherein the sensor board is designed to have aplurality of movable portions formed on one surface thereof, and thecircuit board covers each of the plurality of movable portions throughthe gap portion.
 13. The dynamic quantity sensor according to claim 12,wherein a rim portion abutting against the sensor board is formed at asite on the circuit board facing areas other than the area having theplurality of movable portions formed therein on the sensor board. 14.The dynamic quantity sensor according to claim 9, wherein: a recessportion is formed on a surface of the circuit board facing the sensorboard to thereby form the gap portion; and the bonding portion is formedat sites other than the recess portion on the circuit board.
 15. Thedynamic quantity sensor according to claim 9, wherein the sensor boardis designed to have a plurality of movable portions formed on onesurface thereof, and the circuit board covers each of the plurality ofmovable portions through the gap portion.
 16. The dynamic quantitysensor according to claim 15, wherein a rim portion abutting against thesensor board is formed at a site on the circuit board which faces areasother than the area having the plurality of movable portions formedtherein on the sensor board.
 17. The dynamic quantity sensor accordingto claim 9, further comprising a lead frame for transmitting theelectrical signals to an exterior, wherein an overhang area that doesnot face the sensor board and that overhangs from the sensor board isequipped on the surface of the circuit board that faces the sensorboard, and the lead frame is bonded to the overhang area on the circuitboard.
 18. The dynamic quantity sensor according to claim 9, wherein anoverhang area that does not face the sensor board and that overhangsfrom the sensor board is equipped on the surface of the circuit boardthat faces the sensor board, and a separate board separated from thesensor board is equipped to the overhang area on the circuit board sothat the circuit board is supported by the separate board.
 19. Thedynamic quantity sensor according to claim 9, wherein a plurality ofsensor boards is bonded to the circuit board.
 20. A dynamic quantitysensor comprising: a sensor board including a movable portion at onesurface side thereof, wherein the movable portion is displaced underapplication of a dynamic quantity; and a circuit board for transmittingto and receiving electrical signals from the sensor board, wherein thecircuit board is disposed so as to confront one surface of the sensorboard through a gap portion and to cover the movable portion, andwherein the sensor board and the circuit board are partially bonded toeach other around the gap portion.